Heterodyne circular photodetector array in a tracking system

Abstract

A heterodyne photodetector array, whereby a source beam 32 is reflected off of an object 34 forming a return beam 36 is directed onto an array 48. The array has a centered photodetector cell 52 (FIG. 2) which is surrounded by a plurality of outer photodetector cells 50. The outer cells provide one or more signals for angular tracking of the object, while the center cell provides a signal which may be employed in vibration sensing or other signature measurement applications.

I claim: 
     
       1. Apparatus for angular tracking of an object, comprising: source means, for producing a source beam which is impinged on the object, said source beam is reflected off of the object in the form a return beam;   detector means, having a center photodetector cell disposed in the center of an array, said array having a plurality of outer photodetector cells surrounding said center cell, said center cell and said outer cells comprising means for converting photon energy from said return beam into one or more electrical signals indicative of a positional shift of said return beam on said array; and   direct means, responsive to said electrical signals, for maintaining a predetermined directional relationship between said source means and the object.   
     
     
       2. Apparatus according to claim 1, further comprising an optical means, for directing said return beam onto said array. 
     
     
       3. Apparatus according to claim 1, wherein said outer photodetector cells comprise four identical photodetector cells, each of said outer photodetector cells being adjacent to two other of said outer photodetector cells, one of said outer cells disposed in each quadrant. 
     
     
       4. Apparatus according to claim 1, wherein said array comprises each of said outer cells being separated from each other of said outer cells by a mask, and each of said outer cells is separated from said center cell by said mask. 
     
     
       5. Apparatus for angular tracking of an object, comprising: source means, for producing a source beam which is impinged on the object, said source beam is reflected off of the object in the form a return beam;   reference means, for proving a reference beam;   combine means, for combining said return beam and said reference beam to produce a combined beam;   detector means, having a center photodetector cell disposed in the center of an array, said array having a plurality of outer photodetector cells surrounding said center cell, said center cell and said outer cells comprising means for converting photon energy from said combined beam into one or more electrical signals indicative of a positional shift of said combined beam on said array; and   direct means, responsive to said electrical signals, for maintaining a predetermined directional relationship between said source means and the object.   
     
     
       6. Apparatus according to claim 5, further comprising an optical means, for directing said combined beam onto said array. 
     
     
       7. Apparatus according to claim 5, wherein said outer photodetector cells comprise four identical photodetector cells, each of said outer photodetector cells being adjacent to two other of said outer photodetector cells, one of said outer cells disposed in each quadrant. 
     
     
       8. Apparatus according to claim 5, wherein said array comprises each of said outer cells being separated from each other of said outer cells by a mask, and each of said outer cells is separated from said center cell by said mask. 
     
     
       9. Apparatus for simultaneous angular tracking and signature sensing of an object, comprising: source means, for producing a source beam which is impinged on the object, said source beam is reflected off of the object in the form a return beam;   sensor means, having a center photodetector cell, said center cell being substantially covered by said return beam, said center cell comprising means for converting photon energy from said return beam into an electrical signature signal indicative of an optical signature contained in said return beam;   tracking means, having a plurality of outer photodetector cells surrounding said center cell forming an array, said outer cells having a portion thereof being impinged upon by said return beam, said outer cells comprising means for converting photon energy from said combined beam into one or more electrical tracking signals indicative of a positional shift of said return beam on said array; and   direct means, responsive to said electrical tracking signals, for maintaining a predetermined directional relationship between said source means and the object.   
     
     
       10. Apparatus according to claim 9, further comprising an optical means, for directing said return beam onto said array. 
     
     
       11. Apparatus according to claim 9, wherein said outer photodetector cells comprise four identical photodetector cells, each of said outer photodetector cells being adjacent to two other of said outer photodetector cells, one of said outer cells disposed in each quadrant. 
     
     
       12. Apparatus according to claim 9, wherein said array comprises each of said outer cells being separated from each other of said outer cells by a mask, and each of said outer cells is separated from said center cell by said mask. 
     
     
       13. Apparatus for simultaneous angular tracking and signature sensing of an object, comprising: source means, for producing a source beam which is impinged on the object, said source beam is reflected off of the object in the form a return beam;   reference means, for proving a reference beam;   combine means, for combining said return beam and said reference beam to produce a combined beam;   sensor means, having a center photodetector cell, said center cell being substantially covered by said combined beam, said center cell comprising means for converting photon energy from said combined beam into an electrical signature signal indicative of an optical signature contained in said return beam;   tracking means, having a plurality of outer photodetector cells surrounding said center cell forming an array, said outer cells having a portion thereof being impinged upon by said combined beam, said outer cells comprising means for converting photon energy from said combined beam into one or more electrical tracking signals indicative of a positional shift of said combined beam on said array; and   direct means, responsive to said electrical tracking signals, for maintaining a predetermined directional relationship between said source means and the object.   
     
     
       14. Apparatus according to claim 13, further comprising an optical means, for directing said combined beam onto said array. 
     
     
       15. Apparatus according to claim 13, wherein said outer photodetector cells comprise four identical photodetector cells, each of said outer photodetector cells being adjacent to two other of said outer photodetector cells, one of said outer cells disposed in each quadrant. 
     
     
       16. Apparatus according to claim 13, wherein said array comprises each of said outer cells being separated from each other of said outer cells by a mask, and each of said outer cells is separated from said center cell by said mask. 
     
     
       17. A heterodyne photodetector array, whereupon a spot from a return beam, reflected from an object, is impinged, comprising: sensor means, having a center photodetector cell, said center cell being substantially covered by the spot, said center cell comprising means for converting photon energy from the return beam into an electrical signature signal indicative of an optical signature contained in said return beam; and   tracking means, having a plurality of outer photodetector cells surrounding said center cell forming an array, said outer cells having a portion thereof being impinged upon by the spot, said outer cells comprising means for converting photon energy from the return beam into one or more electrical tracking signals indicative of a positional shift of the spot.   
     
     
       18. A heterodyne photodetector array according to claim 17, wherein said tracking means comprises said other cells having four identical photodetector cells, each of said outer photodetector cells being adjacent to two other of said outer photodetector cells, one cell in each quadrant. 
     
     
       19. A heterodyne photodetector array according to claim 17, wherein said array comprises each of said outer cells being separated from each other of said outer cells by a mask, and each of said outer cells is separated from said center cell by said mask.